designed? The Bureau
squeezes them in its
giant testing machines
as easily as you can
break a graham cracker
or bend a tin can, and
gets the answers engi
neers need. These ma
chines can crush brick
and glass block walls,
stretch steel cables, and
pull apart ship bulk
heads, to find weak
spots.
Though in the United
States we commonly
measure lengths in feet
and weights in pounds,
you will find no stand
ard foot or pound at the
National Bureau of
Standards.
Instead, it
carefully preserves
a
standard meter and a
standard
kilogram,
which are precisely cali
brated against the in
ternational standard
meter and kilogram kept
in Paris. Our foot is
slightly over three-tenths
(.3048) of a meter, and
a pound is 45.36 percent
of a kilogram.
The Bureau's stand
ard meter and kilogram
are guarded in a secure
ly locked vault. The
kilogram
is
never
touched by human
hands, for a spot of per
spiration could alter its
weight.
When the kilogram is
taken out, it is carried
by two men, so that if
one should faint or
stumble the other would
keep it from falling to
758
National Geographic Photographer John E. Fletcher
the floor.
When it is
"Automatic Redcap" Lifts Luggage until the Handles Snap
placed on scales, for
To set quality standards for manufacturers, this machine picks up and sets
checking other weights
down brick-weighted suitcases at the Bureau of Standards. A strong handle,
against it, the operator
it has been determined, should survive 25,000 pickups (page 774).
works by remote control
10 feet away, lest the
sample. Unless he can be sure his sampling heat of his body affect the test (page 783).
pipette contains a known amount of blood,
Though no one ever has seen electricity or
the count is meaningless. Accuracy of such
even knows just what it is,* the Bureau
pipettes is tested by the Bureau.
"weighs" it regularly to get the value of an
Bending Steel Bridge Girders
ampere of current. A small electric coil hung
from one end of a delicate balance is placed
Is a concrete slab six inches thick strong between two larger coils. When current is
enough for a main highway? Will a steel
* See "The Fire of Heaven," by Albert W. Atwood,
bridge girder carry the load for which it is NATIONAL GEOGRAPHIC MAGAZINE, November, 1948.